[Characterization of a canine model of dystrophic bullous epidermolysis (DBE). Development of a gene therapy protocol].

The main human forms of epidermolysis bullosa (EB), namely EB simplex, junctional EB and dystrophic EB, have also been described in domestic animals (small and large ruminants, and horses) and companion animals (cats and dogs). A recent description of dystrophic epidermolysis bullosa (DEB) in Golden Retriever dogs provided details of the principal clinical, morphological and genetic features. The disease is characterized by blisters and erosions in the oral and esophageal epithelia, together with milia, nails dystrophy and growth retardation. The cutaneous lesions regress spontaneously in adult dogs, whereas the epithelial lesions persist, aggravate and spread, notably to the cornea. Classical microscopic studies (light and electron microscopy, indirect immunofluorescence) have revealed anchoring fibril abnormalities and very low-level and heterogenous expression of collagen type VII. The culprit mutation (G1906S) in the canine gene COL7A1 (87.8% nucleotide sequence identity to the human counterpart) involves the replacement of guanine 5716 by adenine, leading to glycine substitution by serine at amino acid position 1906. Transmission in kennels occurs in recessive mode (RDEB). These features recall certain human forms of DEB, and particularly those with a phenotype intermediate between gravis (the so-called Hallopeau-Siemens form) and mitis. No curative treatment of human EB is currently available, and efforts are therefore being made to develop a gene therapy protocol in animals. The first steps have already been successfully achieved, namely the development of a recombinant virus vector able to insert the wild-type gene into the keratinocyte genome, and grafting of artificial skin containing transfected canine keratinocytes in nude mice. The recombinant vectors are Moloney-type retroviruses (MMLV-PCMV), and the Zeocin resistance gene is used to select transduced cells. The artificial skin reconstructed in vitro is of the full-thickness type. Despite the large size of the transduced (9 kb), 95% of cells are transduced and produce large amounts of wild-type collagen. Two key issues remain, however: the possible immunogenicity of the transgene product and the persistence of transgene expression in individuals with a functional immune system. Golden Retriever dogs will provide a suitable animal model for these studies.